This application is based on Patent Application No. 10-376677 (1998) filed Dec. 25, 1998 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink printing method and an ink printing apparatus, and more particularly to the ink printing method and the ink printing apparatus which perform printing by using a processing liquid to promote insolubilization or solidification of a pigment in an ink. The ink printing method and the ink printing apparatus of the present invention are applicable to equipment such as a printer, a copy machine, a facsimile machine or the like, which prints letters, images or the like on a printing medium such as paper or the like, and also as a printing mechanism for such equipment.
2. Description of the Prior Art
To secure a high optical reflection density (hereinafter referred to as xe2x80x9cODxe2x80x9d) has been one of the important technical themes for ink printing. Electrophotography is a printing technique which realizes a relatively high OD, and ink printing has been required to secure an OD as high as that associated with the electrophotography.
The assignee of the present invention has proposed to use a liquid which promotes solidification of a colorant, e.g., dye or pigment, in the ink for improving waterproofness of a printed matter. Such a liquid is hereinafter referred to as a processing liquid. Japanese Patent Application Laid-Open No. 10-226055 (1998) mentions the processing liquid containing polyvalent metallic ions or a high-molecular-weight polymer as the solidification promoter for the colorant, e.g., pigment or dye, in ink. This document discloses a technique to secure uniform images on a printing medium for forward-and-backward printing, where proportion of the processing liquid is reduced in the backward printing than in the forward printing, noting that the image density and dot diameter are different in the forward and backward printing.
The inventors of the present invention have analyzed the images produced by a known ink containing a pigment and the reaction between the processing liquid and the pigment to find that the dot diameter conversely decreases as a reaction between the processing liquid and the pigment proceeds, because of the promoted coagulation or solidification. In other words, increasing coagulation rate and increasing image density are technical objectives which run counter to each other.
The inventors of the present invention, therefore, have concluded that it is necessary to develop a technique which can adequately control at least one of the image quality conditions, e.g., image density, dot shape and dot area, with an ink containing such a pigment.
The inventors of the present invention have found, after having extensively studied, a new technical necessity which cannot be satisfied by first applying the processing liquid to the printing medium, followed by applying the ink droplets. The necessary technique for use of the processing liquid is to create the phenomena of promoting coagulation of the pigment by the reaction with the liquid and, at the same time, diffusing the pigment, to form an image that is excellent in fixation and image quality. It should be noted that these phenomena run counter to each other.
The main object of the present invention is to provide a novel ink printing method and a novel printing apparatus which give, when a pigment-containing ink is used, an image of desired image density.
It is another object of the present invention to provide a novel ink printing method and a novel printing apparatus which form, with the aid of a pigment-containing ink, an image of higher and/or lower density, or image of more multi level of density or more desired tone image than a case when the processing liquid is used in correspondence one-to-one to the ink, while securing the image quality at a high fixation speed.
The ink printing method and the ink printing apparatus of the present invention are mainly characterized by use of a processing liquid of a xe2x80x9chigh penetrativexe2x80x9d (e.g., that satisfies the standard described later) as the one to promote solidification of the pigment and by a smaller quantity of the processing liquid for use than the pigment-containing ink for a unit area, in order to achieve the above objects.
In a first aspect of the present invention, there is provided an ink printing method of forming an image on a printing medium by using an ink containing a pigment, the method comprising the step of:
applying a processing liquid which contains processing material for working to accelerate solidification of the pigment in the ink containing the pigment and shows high penetrability to the ink containing the pigment;
wherein the applying step differentiates applying of the processing liquid per unit area from applying quantity of the ink containing the pigment per unit area to form an image different in density from the image formed on the printing medium with the ink containing the pigment.
In a second aspect of the present invention, there is provided an ink printing method of performing printing by applying a processing liquid which works to accelerate solidification of a pigment after applying ink containing the pigment to a printing medium,
wherein the processing liquid contains an insolubilizer of polymer and is highly penetrative and the processing liquid is applied at 50% or less in quantity of the ink applied to the printing medium.
In a third aspect of the present invention, there is provided an ink printing method, wherein an ink containing a pigment as a colorant and having a penetration coefficient Ka, which is a proportional coefficient for time span after penetration of the ink is started, when quantity of the ink penetrated is proportional to xc2xdth order of, or the square root of, the time span, of less than 1.0 is applied onto a printing medium at a given quantity per unit area, and then a processing liquid coagulating the colorant by the reaction and having the penetration coefficient Ka of 5.0 or more is applied onto the printing medium at a given quantity per unit area.
In a fourth aspect of the present invention, there is provided an ink printing method, wherein an ink containing a pigment as a colorant and having a penetration coefficient Ka, which is a proportional coefficient for time span after penetration of the ink is started, when quantity of the ink penetrated is proportional to the square root of the time span, of less than 1.0 is applied in a thinned out manner onto a printing medium, and then a processing liquid containing an insolubilizer of polymer which coagulates the colorant by the reaction and having the penetration coefficient Ka of 5.0 or more is applied onto the printing medium in a thinned out manner.
In a fifth aspect of the present invention, there is provided an ink printing method of forming an image on a printing medium by using an ink containing a pigment, the method comprising the step of:
applying a processing liquid which contains processing material for working to accelerate solidification of the pigment in the ink containing the pigment and shows higher penetrability to the printing medium than that of the ink, to the ink containing the is pigment.
wherein the applying step differentiates applying of the processing liquid per unit area from applying quantity of the ink containing the pigment per unit area to form an image different in density from the image formed on the printing medium with the ink containing the pigment.
In a sixth aspect of the present invention, there is provided an ink printing apparatus for performing printing by applying a processing liquid which works to accelerate solidification of a pigment after applying ink containing the pigment to a printing medium, the apparatus comprising:
means for applying an ink containing a pigment as a colorant and having a penetration coefficient Ka, which is a proportional coefficient for time span after penetration of the ink is started, when quantity of the ink penetrated is proportional to the square root of the time span, of less than 1.0 is applied in a thinned out manner onto a printing medium, and then applying a processing liquid which coagulates the colorant by the reaction and having the penetration coefficient Ka of 5.0 or more is applied onto the printing medium in a thinned out manner,
wherein the processing liquid contains an insolubilizer of polymer and is highly penetrative and the processing liquid is applied at a given rate of the ink applied to the printing medium.
In a seventh aspect of the present invention, there is provided an ink printing apparatus, wherein an ink containing a pigment as a colorant and having a penetration coefficient Ka, which is a proportional coefficient for time span after penetration of the ink is started, when quantity of the ink penetrated is proportional to the square root of the time span, of less than 1.0 is applied in a thinned out manner onto a printing medium, and then a processing liquid containing an insolubilizer of polymer which coagulates the colorant by the reaction and having the penetration coefficient Ka of 5.0 or more is applied onto the printing medium in a thinned out manner.
In an eighth aspect of the present invention, there is provided an ink printing apparatus for forming an image on a printing medium by using an ink containing a pigment, the method comprising:
image forming means for applying a processing liquid which contains processing material for working to accelerate solidification of the pigment in the ink containing the pigment and shows high penetrability to the ink containing the pigment, the means differentiating applying of the processing liquid per unit area from applying quantity of the ink containing the pigment per unit area to form an image different in density from the image formed on the printing medium with the ink containing the pigment, and
varying applying amount means for varying the quantity of the high penetrative processing liquid per unit area which is applied by the image forming means according to density of an image to be formed.
In a ninth aspect of the present invention, there is provided an ink printing apparatus for forming an image on a printing medium by using an ink containing a pigment, the method comprising:
image forming means for applying a processing liquid which contains processing material for working to accelerate solidification of the pigment in the ink containing the pigment and shows higher penetrability to the printing medium than that of the ink, to the ink containing the pigment, the means differentiating applying of the processing liquid per unit area from applying quantity of the ink containing the pigment per unit area to form an image different in density from the image formed on the printing medium with the ink containing the pigment, and
varying applying amount means for varying the quantity of the high penetrative processing liquid per unit area which is applied by the image forming means according to density of an image to be formed.
According to the above constitution, quantity of the processing liquid relative to the pigment-containing ink is decreased, because the liquid is applied at a restricted rate. Thus, an amount of the product of a reaction between the ink and the processing liquid penetrating deep in the thickness direction of a printing medium becomes smaller. As a result, the product spreads more over the printing medium surface. Therefore, the product tends to be concentrated and fixed in a relatively shallow portion of the medium, allowing the control of OD more easily. Keeping the containing rate of the processing liquid equal to or smaller than 50% of the pigment-containing ink allows an image of high density or conversely of low density, or an image of multiple (xe2x80x9cmultixe2x80x9d) levels of density to be produced.
The xe2x80x9chigh-molecular-weight insolubilizerxe2x80x9d for the present invention is acceptable, when constituent compounds having a molecular weight of 300 or more account for the majority. More preferably, it has an average molecular weight of 500 or more.
xe2x80x9cThinningxe2x80x9d the processing liquid for the present invention may be effected by various methods, so long as it results in supplying a smaller quantity of the liquid than the pigment-containing ink for the unit area printed with the ink. For example, the liquid may be thinned out by the data processing or controlling the ejected quantity of the liquid, or ejected at a predetermined rate.
xe2x80x9cInsolubilizationxe2x80x9d for the present invention includes complete insolubilization, needless to say, promotion of solubilization by the aid of an insolubilizer, and practical insolubilization, i.e., the pigment becomes mostly insoluble (e.g., 80% or more, or 90% or more), although left soluble partly.
The above and other objects, effects, features and advantages of the present invention will become apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.